1) Field of the Invention
The present invention relates to an arrangement for threading a pulp web from the press section of a pulp machine to the dryer of the pulp machine, the arrangement comprising a closing tail threading belt or the like, which is arranged to convey the narrow tail end formed on the pulp web inside the dryer, where the tail threading cord travels outside the edge of the normal web line of the pulp web, which tail end can subsequently be broadened into a normal-width pulp web, the arrangement further comprising means for gripping the tail end in order to bring the tail end inside/between a closing tail threading cord or the like, whereby the gripping means are arranged to function at the normal running speed of the pulp machine.
The invention also relates to a method for threading a pulp web from the press section of a pulp machine to the dryer of the pulp machine, the dryer being provided with a closing tail threading cord or the like, the said tail threading cord conveying the narrow tail end formed earlier on the pulp web inside the dryer, the said tail end being subsequently broadened into a normal-width pulp web, in which method the tail end is conveyed at essentially the normal running speed of the pulp machine between the tail threading cord using means to convey the tail end a desired distance inside/between the closing tail threading cord or the like.
2) Description of Related Art
In a typical pulp machine, from the headbox of the pulp machine is fed pulp onto the wire section, which pulp is dewatered in such a way that the dry matter content of the pulp web is approximately 20%, and after the wire section the pulp web is conveyed through the press section, where the dry matter content is increased to a value of approximately 50%. After the press section, the pulp web is typically dried in an air dryer, in which the pulp web travels through layers that are on top of each other from the top part of the dryer to its bottom part alternately from the forward end to the tail of one layer and from the tail of the next layer to its forward end, etc. The drying layers are formed by means of rows of blow boxes, whereby in each layer, the air nozzles in the blow boxes are directed, for example, towards each other and the pulp web travels on a route between the said air nozzles facing each other. The length of the route travelled by the pulp web in the air dryer is typically within the range from about 500 to 1000 m, depending on the length of the dryer, which is typically about 20 to 50 m, and on the number of layers, which may be, for example, 10 to 30. Typically, the pulp web travels as an open draw from the press section to the dryer section. To facilitate the feeding of the pulp web from the press section to the dryer, a narrow tail end cut on the edge of the pulp web before the press section is used, which is conveyed inside the dryer by means of the closing tail threading cord running adjacent to the drying route, and typically through the entire dryer, before the tail end is broadened to its full web width.
Once the pulp web has been broadened to the normal web width, the use of the tail threading cord is discontinued and the pulp web will travel drawn by the drawing rolls in the dryer as an open draw from the press nip N to the top part of the dryer. The lifting height of the open draw of the pulp web is typically of the order of about 5 m. In a prior art arrangement, the threading of the tail end typically takes place manually, which can be carried out at the normal running speed of the pulp machine only in relatively slow pulp machines having a running speed of, for example, below about 150 m/min. In current pulp machines, where the running speed may exceed about 250 m/min, to be able to convey the tail end manually inside the tail threading cord during the tail bringing stage, the speed of the pulp machine must be kept substantially lower than the normal running speed. Furthermore, this type of manual bringing requires considerable professional skill and includes a risk of injury should one's hand for some reason be left inside the closing tail threading cord. The functioning of a closing tail threading cord is previously known, and one solution for opening and closing a closing tail threading cord inside the tail end to enable feeding is disclosed in FI-patent no. 55882. In connection with the present application, the term “closing tail threading cord or the like” includes, for example, in addition to the closing tail threading cord disclosed in the FI-patent 55882, also tail threading arrangements known as such comprised of endless rope-, chain-, or band-like means, in which the tail threading cord is pressed between two or more rope-, chain-, or band-like means.
The aim of the invention is, therefore, to provide as fully automated a method as possible for threading a pulp web from the press section to the dryer. One solution for conveying the tail end mechanically inside the tail threading cord is disclosed in a previous application FI 981449 by the Applicant of the present application, where, however, one significant problem was considerable lateral shift of the order of 400 mm. The wet end of the pulp web does not withstand lateral “twisting”, but will tear easily, whereas it withstands straight pulling by its own weight over several metres. To solve this problem, the arrangement according to the invention for threading a pulp web from the press section to the dryer is characterised in that the arrangement comprises means by which the tail threading cord can be moved inwards from its normal route, towards the pulp web, to travel essentially in the same line with the tail end formed on the edge of the pulp web before the tail end is conveyed inside the tail threading cord, and means by which the tail threading cord and the tail end inside it can be moved back to the normal route located outside the edge of the pulp web before entering the dryer.